Epoxy Core With Expandable Microspheres

ABSTRACT

A method of fabricating a formed structure with expandable polymeric shell microspheres. A first plurality of polymeric shell microspheres are heated from an unexpanded state to an expanded state to form a plurality of expanded microspheres. The plurality of expanded microspheres are mixed with an epoxy resin and a second plurality of unexpanded polymeric shell microspheres. The mixture is formed in a shape to create a preform. The preform is wrapped with fiber tape to create a wrapped preform. The wrapped preform is placed in a mold. The mold is heated and the second plurality of unexpanded microspheres expand from an unexpanded state to an expanded state. The mold is cooled and the formed structure is removed from the mold.

FIELD OF THE INVENTION

This invention relates generally to fabrication of molded structures.More particularly, aspects of this invention relate to hockey bladesmolded from a core that includes expandable thermoplastic microspheres.

BACKGROUND

Typical hockey stick blades are generally made of a core reinforced withone or more layers of synthetic materials such as fiberglass, carbonfiber or Aramid. The core of the blade may also be made of a syntheticmaterial reinforced with layers of fibers.

The layers may be made of a woven filament fiber, preimpregnated withresin. Prior art structures have included a foam core with a piece offiber on the front face of the blade and a second piece of fiber on therear face of the blade, in the manner of pieces of bread in a sandwich.

SUMMARY

The following presents a general summary of aspects of the invention inorder to provide a basic understanding of the invention and variousfeatures of it. This summary is not intended to limit the scope of theinvention in any way, but it simply provides a general overview andcontext for the more detailed description that follows.

Aspects of this invention relate to systems and methods for fabricatinga formed structure. In one aspect of the invention, a formed structureis fabricated with expandable polymeric shell microspheres. A firstplurality of polymeric shell microspheres are heated from an unexpandedstate to an expanded state to form a plurality of expanded microspheres.The expanded microspheres are mixed with a plurality of expandedmicrospheres with an epoxy resin and a second plurality of unexpandedpolymeric shell microspheres to create a mixture. The mixture is formedin a shape such a hockey stick blade to create a preform. The preform iswrapped with fiber tape preimpregnated with resin to create a wrappedpreform. The wrapped preform is placed in a mold. The mold is heated,expanding the second plurality of unexpanded microspheres from anunexpanded state to an expanded state. The mold is cooled and the formedstructure is removed from the mold.

The preform comprises a first face surface, a second face surface, afirst edge surface and a second edge surface, and the fiber tape extendscontinuously around the first face surface, the first edge surface, thesecond face surface and the second edge surface. The mixture furthercomprises a chopped fiber and a curing agent.

In another aspect of the invention, a first plurality of polymeric shellmicrospheres are heated from an unexpanded state to a partially expandedstate to form a plurality of expanded microspheres. The partiallyexpanded microspheres are mixed with a plurality of expandedmicrospheres with an epoxy resin and a second plurality of unexpandedpolymeric shell microspheres to create a mixture. The mixture is formedin a shape such a hockey stick blade to create a preform. The preform iswrapped with fiber tape preimpregnated with resin to create a wrappedpreform. The wrapped preform is placed in a mold. The mold is heated,expanding the first plurality of partially expanded microspheres and thesecond plurality of unexpanded microspheres from an unexpanded state toan expanded state. The mold is cooled and the formed structure isremoved from the mold.

The preform comprises a first face surface, a second face surface, afirst edge surface and a second edge surface, the tape extendingcontinuously around the first face surface, the first edge surface, thesecond face surface and the second edge surface. The mixture furthercomprises chopped fiber and a curing agent.

Another aspect of the invention is an expandable core comprising epoxy,a curing agent, gas encapsulated polymeric shell microspheres expandedby heating to a diameter of about 40-50 microns, and unexpanded,expandable gas encapsulated polymeric shell microspheres about 10-12microns in diameter. The core further includes chopped fiber.

Other objects and features of the invention will become apparent byreference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and certainadvantages thereof may be acquired by referring to the followingdetailed description in consideration with the accompanying drawings, inwhich:

FIG. 1 generally illustrates an isometric side view of a core formed inthe shape of a blade and wrapped with tape;

FIG. 2 is an isometric side view of the core with a cross sectional viewtaken along line 2-2 of FIG. 1;

FIG. 3 is a flow diagram illustrating steps of a process to fabricate ablade in accordance with an exemplary embodiment;

FIG. 4 is a flow diagram illustrating steps of a process to fabricate ablade in accordance with another exemplary embodiment.

FIG. 5 is an isometric side view of a core formed in the shape of ablade and wrapped with tape in a configuration different than that ofFIG. 1; and

FIG. 6 is an isometric side view of a core formed in the shape of ablade and wrapped with tape in a configuration different than that ofFIG. 1 and FIG. 5;

The reader is advised that the attached drawings are not necessarilydrawn to scale.

DETAILED DESCRIPTION

In the following description of various example structures in accordancewith the invention, reference is made to the accompanying drawings,which form a part hereof, and in which are shown by way of illustrationvarious structures in accordance with the invention. Additionally, it isto be understood that other specific arrangements of parts andstructures may be utilized, and structural and functional modificationsmay be made without departing from the scope of the present invention.Also, while the terms “top” and “bottom” and the like may be used inthis specification to describe various example features and elements ofthe invention, these terms are used herein as a matter of convenience,e.g., based on the example orientations shown in the figures and/or theorientations in typical use. Nothing in this specification should beconstrued as requiring a specific three dimensional or spatialorientation of structures in order to fall within the scope of thisinvention.

In general, as described above, aspects of this invention relate tosystems and methods for fabricating a structure, such as a hockey stickblade. More detailed descriptions of aspects of this invention follow.

FIG. 1 illustrates a side view of an epoxy core 20 formed in the shapeof a blade and wrapped with tape 22. FIG. 2 is a cross sectional viewtaken along line 2-2 of FIG. 1, which shows the tape 22 wrappedcontinuously around the core 20.

The epoxy core 20 is formed with microspheres. In one embodiment,“Expancell” microspheres are used. In the formation of thesemicrospheres, a drop of a hydrocarbon, liquid isobutene, is encapsulatedin a gasproof, polymeric thermoplastic shell. When this microsphere isexposed to heat, the shell softens and the hydrocarbon inside the shellincreases its pressure, expanding the shell. Before expansion, thediameter of the microsphere is typically 10-12 um and the density is1000-1200 kg/m3. After expansion, the diameter of the microsphere is40-50 um and the density decreases to 20-30 kg/m3.

The temperature at which expansion starts as well as the temperature atwhich the maximum expansion and the lowest density is obtained dependson a variety of factors including the rate of heating of the shells. Attemperatures above the temperature at which the highest expansion isobtained the microspheres gradually collapse.

The microspheres are highly resilient. The expanded microspheres areeasy to compress. Due to this resiliency, the microspheres can withstandcycles of loading/unloading without collapsing or breaking. Thisproperty is important for use in shock absorbent materials.

Thermoplastic microspheres are distinct from glass microballoons. Glassmicroballoons are heavier than thermoplastic microballoons.Additionally, glass microballoons do not exhibit the same dampeningproperties as thermoplastic microballoons. For these reasons,thermoplastic microspheres are preferred over glass microballoons in themanufacture of hockey stick blade, which must be lightweight, flexibleand capable of withstanding considerable forces.

As a first step in one embodiment of the process, a group of expandablemicrospheres are heated and they expand from their original size to anexpanded size. The expanded microspheres have a diameter of 60-120 um.

The expanded microspheres are then mixed with unexpanded microspheres.This combination of expanded and unexpanded microspheres is mixed withan epoxy material, such as Epon828. Other strengthening materials, suchas aramid pulp, chopped fiber glass or chopped carbon fiber are alsoadded to the mixture. Carbon nanotubes can also be added enhancestiffness and shear strength. A curing agent is also added to themixture. The final epoxy mixture has the consistency of modeling clay.

The mixture of the expanded microspheres, the unexpanded microspheres,the epoxy, the other strengthening materials and the curing agent isthen formed in the shape of a preform, such as a hockey blade. As shownin FIG. 2, the preform has a first face surface 30, a first edge 32, asecond face surface 34, and a second edge 36.

The structure is then wrapped with carbon fiber tape 22. The carbonfiber tape 22 is preimpregnated with resin. The tape 22 is wrappedcontinuously around the first face surface 30, the first edge 32, thesecond face surface 34 and the second edge 36. This continuous wrappingof the preform 20 with the tape 22 results in a first wrapped face 40, asecond wrapped face 44, a top wrapped edge 42 and a bottom wrapped edge46.

The tape may be wrapped in various configurations around the core, suchas shown in FIG. 5 and FIG. 6. The tape may be wrapped at a 30 or 45degree angle to the longitudinal axis of the blade, as shown in FIG. 5.A second layer of preimpregnated may be wrapped at a 90 degree angle tothe tape, as shown in FIG. 6.

As shown in FIG. 1, the core includes a toe 45. The tape 22 extendsaround the entire core, to the end of the toe 45, but for purposes ofmore clearly illustrating the invention in FIG. 1, the tape 22 is notshown extending to the end of the toe 45 of the core.

The use of tape wrapped continuously around the entire epoxy preformcore, including the edges, is advantageous over a sandwichconfiguration, where the tape does not continuously extend of over theedges, for several reasons. A hockey blade must be very durable andcapable of withstanding large forces from a variety of directions. Forexample, the hockey blade can encounter considerable forces, such asfrom striking a puck or the surface of the ice in multiple manners andangles. Thus, the core needs reinforcement in all directions. The wrapconfiguration results in a torsionally stiffer and stronger structure.The wrap configuration also is better able to withstand shear forces.

The wrapped structure is then placed in a mold. The mold is heated to anappropriate temperature. In one embodiment, the mold is heated to 140degrees C. Upon heating, the epoxy softens. Additionally, the unexpandedmicrospheres expand with this additional hearing. The epoxy,microspheres, the other materials bond to each other and also bond tothe carbon fiber tape in the mold.

The mold is cooled and the formed blade is removed from the mold.

The unexpanded microspheres are required to produce enough pressure onthe outer walls of the structure. Without sufficient pressure during themolding process, the walls will be wrinkled and/or have large numbers ofvoids and/or other imperfections.

The expanded microspheres increase the viscosity of the material, makinga more stable pre-form during the kitting operation. Also, the expandedmicrospheres allow for a larger volume pre-form, which is closer to thefinal geometry of the part. This is advantageous because it allows lessmovement (and more precision) of the structural fibers during themolding process.

The combination of expanded and unexpanded (or partially expanded) isimportant because it provides a high viscosity material which producesenough pressure to compress/consolidate the carbon fibers walls aroundit.

In one embodiment, the core comprises the following materials(parts/weight):

-   -   Base epoxy (Epon 828): 100    -   Chopped fiber, e.g., Aramid Pulp 3091 (from Teijin): 2.5    -   Hardener (curing agent): 14.82    -   Expancel (pre-expanded) 092DET80d20: 2    -   Expancel (unexpanded) 051DU40: 2.5

The steps of this embodiment of the process are illustrated in FIG. 3.As shown at 202, a first plurality of polymeric shell microspheres areheated from an unexpanded state to an expanded state to form a pluralityof expanded microspheres. As shown at 204, the plurality of expandedmicrospheres are mixed with an epoxy resin, chopped fiber, curing agentand a second plurality of unexpanded polymeric shell microspheres tocreate a mixture. The mixture is formed in a shape to create a preform,such as a hockey blade, as shown at 206. The preform is wrapped withfiber tape to create a wrapped preform as shown at 208. The preformcomprises a first face surface, a second face surface, a first edgesurface and a second edge surface, and the fiber tape extendscontinuously around the first face surface, the first edge surface, thesecond face surface and the second edge surface. The wrapped preform isplaced in a mold as shown at 210. The mold is heated and the secondplurality of unexpanded microspheres expand from an unexpanded state toan expanded state as shown at 212. The mold is cooled as shown at 214,and the formed structure is removed from the mold as shown at 216.

As a first step in another embodiment of the process, a group ofexpandable microspheres are heated and they partially expand from theiroriginal size to a larger size, but not to their full size. Thepartially expanded microspheres have a diameter of 60-90 um.

The partially expanded microspheres are then mixed with unexpandedmicrospheres. This combination of partially expanded and unexpandedmicrospheres is mixed with an epoxy material, such as Epon828. Otherstrengthening materials, such as aramid pulp, chopped fiber glass orchopped carbon fiber are also added to the mixture. Carbon nanotubes canalso be added enhance stiffness and shear strength. A curing agent isalso added to the mixture. The final epoxy mixture has the consistencyof modeling clay.

The mixture of the partially expanded microspheres, the unexpandedmicrospheres, the epoxy, the other strengthening materials and thecuring agent is then formed in the shape of a preform, such as a hockeyblade. As shown in FIG. 2, the preform has a first face surface 30, afirst edge 32, a second face surface 34, and a second edge 36.

The structure is then wrapped with carbon fiber tape 22. The carbonfiber tape is preimpregnated with resin. The tape is wrappedcontinuously around the first face surface 30, the first edge 32, thesecond face surface 34 and the second edge 36. This continuous wrappingof the preform 20 with the tape 22 results in a first wrapped face 40, asecond wrapped face 44, a top wrapped edge 42 and a bottom wrapped edge46.

The use of tape wrapped continuously around the entire epoxy preformcore, including the edges, is advantageous over a sandwichconfiguration, where the tape does not continuously extend of over theedges, for several reasons. A hockey blade must very durable and capableof withstanding large forces from a variety of directions. For example,the hockey blade can encounter considerable forces, such as fromstriking a puck or the surface of the ice in a multiple manners andangles. Thus, the core needs reinforcement in all directions. The wrapconfiguration results in a torsionally stiffer and stronger structure.The wrap configuration also is better able to withstand shear forces.

It is to be understood that the tape need not consist of a singleunitary piece or sheet of material. For example, the tape can consist ofa combination of multiple pieces or sheets that overlap.

The wrapped structure is then placed in a mold. The mold is heated to anappropriate temperature. In one embodiment, the mold is heated to 140degrees C. Upon heating, the epoxy softens. Additionally, the unexpandedmicrospheres, as well as the microspheres that previously were partiallyexpanded, expand further with this additional hearing. The epoxy,microspheres, the other materials bond to each other and also bond tothe carbon fiber tape in the mold.

The mold is cooled and the formed blade is removed from the mold.

The steps of this embodiment of the process are illustrated in FIG. 4.As shown at 302, a first plurality of polymeric shell microspheres areheated from an unexpanded state to a partially expanded state to form aplurality of expanded microspheres. As shown at 304, the plurality ofexpanded microspheres are mixed with an epoxy resin, chopped fiber,curing agent and a second plurality of unexpanded polymeric shellmicrospheres to create a mixture. The mixture is formed in a shape tocreate a preform, such as a hockey blade, as shown at 306. The preformis wrapped with fiber tape to create a wrapped preform as shown at 308.The preform comprises a first face surface, a second face surface, afirst edge surface and a second edge surface, and the fiber tape extendscontinuously around the first face surface, the first edge surface, thesecond face surface and the second edge surface. The wrapped preform isplaced in a mold as shown at 31O. As shown at 312, the mold is heated,and the first plurality of partially expanded microspheres expand to anexpanded state, and the second plurality of unexpanded microspheresexpand from an unexpanded state to an expanded state. The mold is cooledas shown at 314, and the formed structure is removed from the mold asshown at 316.

In alternative embodiment, different combinations of core materials areused to create distinct recipes of core mixtures. The different mixturescan be used to create a blade with zones of varying density andstiffness. The bottom of the blade and the heel of the blade aretypically subject to the most force and impact from striking the ice ora hockey puck. Core mixtures with higher density materials can be placedin the areas of the blade subject to greater forces and impacts, such asthe bottom or heel, to create stronger blade regions.

In an alternative embodiment, the core is formed with the epoxy,microspheres and other materials as described, and additionally with afoam insert. The foam insert may be a polymethacrylimide (PMI) foam suchas manufactured under the name Rohacell. A suitable low density PMI foamis RIMA (Resin Infusion Manufacturing Aid) foam. This type of foam is ahigh strength foam that can withstand the shear and impact forces thatresult when a hockey blade strikes a hockey puck. The foam is placed onvarious locations of the blade to create a blade with zones of varyingdensity. The foam may be placed along the top or the toe of the blade toreduce weight.

The reader should understand that these specific examples are set forthmerely to illustrate examples of the invention, and they should not beconstrued as limiting the invention. Many variations in the connectionsystem may be made from the specific structures described above withoutdeparting from this invention.

While the invention has been described in detail in terms of specificexamples including presently preferred modes of carrying out theinvention, those skilled in the art will appreciate that there arenumerous variations and permutations of the above described systems andmethods. Thus, the spirit and scope of the invention should be construedbroadly as set forth in the appended claims.

1. A method of fabricating a formed structure with expandable polymericshell microspheres, comprising: heating a first plurality of polymericshell microspheres from an unexpanded state to an expanded state to forma plurality of expanded microspheres; mixing the plurality of expandedmicrospheres with an epoxy resin and a second plurality of unexpandedpolymeric shell microspheres to create a mixture; forming the mixture ina shape to create a preform; wrapping the preform with fiber tape tocreate a wrapped preform; placing the wrapped preform in a mold; heatingthe mold and expanding the second plurality of unexpanded microspheresfrom an unexpanded state to an expanded state; cooling the mold; andremoving the formed structure from the mold.
 2. The method according toclaim 1 wherein the formed structure is a hockey blade.
 3. The methodaccording to claim 2 wherein said fiber tape is preimpregnated withresin.
 4. The method according to claim 3 wherein the preform comprisesa first face surface, a second face surface, a first edge surface and asecond edge surface, and the fiber tape extends continuously around thefirst face surface, the first edge surface, the second face surface andthe second edge surface.
 5. The method according to claim 4 wherein themixture further comprises a chopped fiber and a curing agent.
 6. Amethod of fabricating a formed structure with expandable thermoplasticmicrospheres, comprising: heating a first plurality of unexpandedthermoplastic microspheres from an unexpanded state to a partiallyexpanded state to form a plurality of partially expanded microspheresmixing the plurality of partially expanded microspheres with an epoxyresin and a second plurality of unexpanded thermoplastic microspheres tocreate a mixture; forming the mixture in a shape to create a preform;wrapping the preform with fiber tape to create a wrapped preform;placing the wrapped preform in a mold; heating the mold and furtherexpanding the plurality of partially expanded microspheres and expandingthe second plurality of unexpanded microspheres; cooling the mold;removing the formed structure from the mold.
 7. The method according toclaim 6 wherein the formed structure is a hockey blade.
 8. The methodaccording to claim 7 wherein said mixture further comprises fiber tapepreimpregnated with resin.
 9. The method according to claim 8 whereinthe preform comprises a first face surface, a second face surface, afirst edge surface and a second edge surface, the tape extendingcontinuously around the first face surface, the first edge surface, thesecond face surface and the second edge surface.
 10. The methodaccording to claim 9 wherein the mixture further comprises chopped fiberand a curing agent.
 11. An expandable mixture comprising epoxy, a curingagent, gas encapsulated polymeric shell microspheres expanded by heatingto a diameter of about 40-50 microns, and unexpanded, expandable gasencapsulated polymeric shell microspheres about 10-12 microns indiameter.
 12. The expandable foam according to claim 11, furthercomprising chopped fiber.
 13. A composite article comprising a foam corewrapped with a tape, the article fabricated by the following steps:heating a first plurality of unexpanded thermoplastic microspheres froman unexpanded state to a partially expanded state to create plurality ofpartially expanded microspheres; mixing the plurality of partiallyexpanded microspheres with an epoxy resin and a second plurality ofunexpanded thermoplastic microspheres to create a mixture; forming themixture in a shape to create a preform; wrapping the preform with fibertape to create a wrapped preform; placing the wrapped preform in a mold;heating the mold and further expanding the plurality of partiallyexpanded microspheres and expanding the second plurality of unexpandedmicroshperes; cooling the mold; and removing the formed structure fromthe mold.
 14. The article according to claim 13 wherein the formedstructure is a hockey blade.
 15. The article according to claim 14wherein the mixture further comprises fiber tape preimpregnated withresin.
 16. The article according to claim 15 wherein the preformcomprises a first face surface, a second face surface, a first edgesurface and a second edge surface, the tape extending continuouslyaround the first face surface, the first edge surface, the second facesurface and the second edge surface.
 17. The article according to claim16 wherein the mixture further comprises chopped fiber and a curingagent.